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Oscar

On 6/5/2012 7:12 PM, wrote:
On Tue, 05 Jun 2012 10:28:52 -0400, wrote:

The facts:
9'X5' inflatable with inflatable keel and hard floor.
5hp 4 stroke engine.
7 1/2 X 7 3 blade prop.

Here's what's happening:
Engine runs smooth as silk.
At about 1/2 throttle GPS measures 4 1/2 MPH
At full throttle GPS measures a little over 5MPH
There is no noticeable change in pitch or DB between 1/2 and full throttle.
Engine doesn't seem to be bogging down.
Speed increase between 1/2 and full throttle is gradual even though
throttle is advanced quickly.
Boat bottom is clean.
Prop is in excellent shape.

Questions:
Is this normal?
Should I try a lower pitched prop?
Do I need more Horsepower?
What do you think?

If you have any V in the floor, 5 HP should be enough to just get
about 600 pounds up on plane.

I would be interested in assessing the RPM at full throttle, before
making a judgment on HP considerations.

A tach wouldn't tell me anything more useful than my ears have already
determined. I'm positive that WOT RPM is way too low.